内蒙古白乃庙铜矿区含矿中酸性侵入岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及成矿时代

A tentative discussion on zircon U-Pb geochronology and geochemistry of ore-bearing intermediate-acid intrusive rocks in the Bainaimiao copper ore district and the metallogenic epoch

为了限定白乃庙铜矿的成矿时代和成矿环境,对含矿中酸性岩类进行同位素年龄和岩石地球化学研究。获得的3个含矿花岗闪长岩样品的LA-MC-ICP-MS锆石U-Pb年龄分别为421.5±1.8Ma、438.6±3.4Ma和459.3±3.6Ma。含矿中酸性岩类属于过铝质钙碱性系列岩石,稀土元素曲线显示为轻稀土元素富集型,具有弱正Eu异常,微量元素曲线表现为明显的Ta、Nb亏损。综合含矿中酸性岩类时代、地球化学特征及区域构造背景,认为白乃庙铜矿总体形成于早古生代,具有多期成矿的特点,成矿作用与古蒙古洋早古生代俯冲消减事件有关。

In order to determine the metallogenic epoch and ore-forming environment of the Bainaimiao copper deposit,the authors carried out research on isotope geochronology and geochemistry of ore-bearing intermediate-acid rocks. LA-MC-ICPMS zircon U-Pb dating shows that the ages of three ore-bearing granodiorites samples are 421.5±1.8Ma,438.6±3.4Ma and 459.3±3.6Ma respectively. These rocks have peraluminous calc-lkaline characteristics,and are enriched in LREE. There is a weak positive anomaly of Eu. The trace elements are obviously depleted in Ta and Nb. According to comprehensive ages and geochemical characteristics of ore-bearing granodiorites and the regional tectonic background,the authors consider that the Bainaimiao copper deposit was on the whole formed in the early Paleozoic and characterized by multi-period mineralization. In addition,the metallogenesis was related to the subduction event of ancient Mongolia Ocean in the Early Paleozoic.